1. Field of The Invention
The present invention relates to free piston engines, and more particularly, to a control system which supplies ignition timing, injection timing, and compression ratio modification information to operate the engine.
2. Brief Description of The Prior Art
Free piston engines are well known in the art. U.S. Pat. Nos. 4,896,632; 4,782,796 and 4,046,115 to Anton Braun, illustrate engines of this type.
It is important to recognize that free piston engines lack both the crankshaft and flywheel structures, which are found in more conventional engines.
The absence of a crankshaft introduces additional degrees of freedom into the operation of free piston engines, and both the stroke length and compression ratio are variables which may be adjusted in a free piston engine.
The absence of a flywheel, limits the amount of energy stored in the system to the relatively small amount of energy which may be stored in the compressor section of the system. This factor renders the free piston engine more sensitive to transient or irregular operating conditions, than crank based engines. For example, in certain free piston engines, a single misfire can cause the engine to stop running.
The absence of a crankshaft and flywheel assembly, also eliminates convenient access to piston position information. This has rendered ignition timing and injection timing parameters difficult to accommodate, in free piston engines. As a consequence, stable engine operation has been difficult to achieve.
These problems are well known in the art and several of them have been addressed. For example, one approach to controlling the ignition timing of a free piston engine, is know from U.S. Pat. No. 3,673,999 to Lacy and Byrne. In this engine, a magnet is coupled to the reciprocating rod of the engine. The magnet moves past the fixed coil which converts rod motion into a velocity dependent voltage signal. In this prior art arrangement, the AC waveform produced by the coil is used to determine the stroke reversal point of the engine. The stroke reversal point is taken as the appropriate ignition timing mark for the engine.
Another approach to controlling ignition timing in a free piston engine is known from U.S. Pat. No. 3,643,638 to Anton Braun. This patent teaches the use of a secondary engine parameter to determine the piston stroke reversal point for ignition timing.
However in spite of these advances, the ability to regulate and control a free piston engine in response to variations in load, as well as the ability to compensate for irregular operating conditions, have proved difficult in this art and has limited the acceptance of this type of engine.